Two-step black color anodizing w/tin sulfate
A discussion started in 2003 & continuing through 2017 -- add your Q to bring it back to the Hot Topics page.(2003)
Q. Could Tin sulfate be used for coloring (black) aluminum utensils (AA3003 alloy) in hard anodizing process? If yes, is it harmful for health.Yasar Bayraktar
- Seydisehir, Konya, Turkey
tin sulfate is a green chemical, not harmful. But blackening with that is not an easy technique.
It's better to trial first according to additional chemical, concentration, timing and current density used.
- bangka island, indonesia
Q. I purchase an anodizing service loosely described as "two step" in my specifications, which also refer to tin sulfate in the process. The anodizer who currently provides this service tells me that the tin sulfate is the second step and provides the black finish my parts have after processing (the first step is merely a clear anodize). I am not familiar with this process and would like to know if a)it is commonly known by another name, b)if it's a relatively common process that can be found globally (my primary machining supplier is in Singapore and I would like to see if he can provide parts complete) and c)if the minimum lot charge of nearly double what I pay for my other anodizing jobs is justified. Thanks in advance for any assistance that might be provided.Fred Tafel
- Mentor, Ohio, USA
by Robert Probert
The Chromating - Anodizing - Hardcoating Handbook
A. Anodizing without subsequent dying produces "clear" aluminum colored parts, Fred, assuming the aluminum is quite pure. If the alloy is rich in copper or silicon, even clear anodizing will come out gray to charcoal.
Anodized parts can be dyed with organic dyes (rather similar to clothes dye but optimized for aluminum), but such colors are not completely lightfast . . . sometimes not very lightfast at all. For greater lightfastness, metal salts are electrolytically deposited at the base of the anodizing pores, and this is called two-step anodizing. And yes, every anodizing shop should have at least a general understanding of the concept even though most probably don't offer it themselves.
Two-step anodizing involves this second electrolytic process and it may also involve a subsequent organic dye to get a fully saturated color as well. It is a premium process, and not all shops are set up to be able to do it, so it will be more expensive. It's hard to say from a distance whether "nearly double" is the right price, but it doesn't seem to be the manifestly wrong price.
Anodizers apply their decades of experience to get you a good finish, so don't make the mistake of thinking anybody can do it, and easily. That is not to assert that there are no shops in and around Singapore with the requisite experience, but it is to say that you shouldn't let a shop "try their hand" at it. You need to find a shop which already does two-step anodizing and you need to have sample parts that they produced in hand before making commitments. Good luck.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Q. DC/AC equipment for colour anodizing? I am looking for information on how to specify ripple, control, etc.to get the best choice for electro coloring anodizing in tin sulfate solutions.
Thank you, very much.Gustavo C. Giraudo
A. I think such specifications are confidential information of manufacturers of AC/DC equipment who have spent a lot of money to develop them..
The best way to have such equipment is to contact with the AC/DC power suppliers' manufacturers and buy a suitable one.Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey
A. I slightly and respectfully disagree with Mr. Ulucak just a bit, because there are some people who feel that complicated and expensive proprietary waveforms are a waste of money in tin-based electrocoloring, and that all that is required is low voltage AC. So I think that the starting point is to hear that side of the issue before listening to sales pitches about the benefits of special waveforms.
"Electrolytic Coloring of Anodized Aluminum Using Tin Electrolytes" by Gohausen & Schoener (Plating & Surface Finishing, Feb. 84) is a great intro to the topic. Best of luck.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Tin sulphate concentration in electrolytic coloring bath jumps up & downJune 16, 2017
Q. Dear finishing team ,
I am a laboratory technical in aluminum extrusion company
I want to ask about coloring bath , it must be (17-19)g/l concentrated of SnSO4 ,and we reach this level of concentration but suddenly it dropped down to 13 and can't make it rise to 17 anymore , we added a lot of gallons to repair it but it still 13-14 g/l
after two months it repair it self and give us 17-19 g/l concentration without we do any thing to it !
Now a days we have this problem again , the concentration dropped to 14 g/l, we added 10 gallons which is 25kg for each gallon then the concentration rise to 16
next day we add 6 gallons and it still 16 ! we added another 6 gallons in the next day and it still 16 !
I hope to find justification for this and what should we do !
engineer - Amman, Jordan
Why does electrolytic coloring use AC current?June 19, 2017
Q. I have a question about electrolytic coloring on anodized aluminium. Why this process use AC to deposit color? In my understand I think this technique like a electrolytic deposition technique that use DC to do. And I would like to tell you that I very new in this field especially about electric so I would like to apologize you if my question is like a stupid question. And the second is if I do some experiment what is the criteria to choose AC or DC to do? Because I'm very confuse about that like a electrolytic coloring technique that I mention above.
Thank you everyone to suggest me ^^.
- Bangkok. Thailand